When a radio technology evolves by introducing new features, it is typically desirable that later versions of the radio technology are backward compatible with earlier versions. In this way, both versions can coexist in the same radio communication system.
An example of such evolution of a radio technology is the LTE (Long Term Evolution) cellular radio technology specified by 3GPP (3rd Generation Partnership Project). Here, for example a user equipment (UE) according to the LTE Release 8 (Rel-8) specifications and a UE according to the LTE Release 10 (Rel-10) specifications may coexist in a cellular network according to the LTE Rel-10 specifications. Further, a UE according to the LTE Rel-10 specifications could utilize a cellular network according to the LTE Rel-8 specifications.
One exemplary difference between the cellular radio technology according to LTE Rel-8 and the cellular radio technology according to LTE Rel-10 resides in the utilization of reference signals. In LTE Rel-10 Channel State Information Reference Signals (CSI-RS) are defined for the purpose of providing Channel State Information (CSI). As compared to that, in LTE Rel-8, CSI measurements rely on Cell-specific Reference Signals (CRS). A UE supporting LTE Rel-10 (in the following also referred to as Rel-10 UE) is aware when and where the CSI-RS are present in the received signals. However, such awareness is not present in the case of a UE supporting only LTE Rel-8 (in the following also referred to as Rel-8 UE). As a result, it may occur that the Rel-8 UE assumes that data is present in resource elements that are used for transmitting the CSI-RS. Thus, if the Rel-8 UE would be scheduled for a transmission in a subframe which contains CSI-RS, the transmission would probably fail. While this problem could be mitigated by not scheduling Rel-8 UEs in subframes containing CSI-RS, such exclusion of subframes for an entire class of UEs may be unduly limiting. Further, also the possibility of configuring zero-power CSI-RS as specified in 3GPP TS 36.213 V12.5.0 (2015-03) does not help, because it only allows for configuring certain predefined CSI-RS constellations as zero power and is not supported for Rel-8 UEs.
In a similar manner, features of an earlier version of a radio technology may have an impact on a later version of this radio technology. For example, the CRS of LTE Rel-8 are typically not needed when performing radio communication with Rel-10 UEs. On the other hand, transmission of the CRS may not be deactivated because Rel-8 UEs rely on them. If the CRSs are not present in a cell, this may prevent a Rel-8 UE from connecting to this cell. As a result, the CRSs typically need to be transmitted in all subframes and all Physical Resource Blocks (PRBs), even if currently no Rel-8 UEs are present in the system. Such requirement of continued transmission of certain signals may constitute a significant limitation, e.g., with respect to energy efficiency or efficiency of resource utilization.
Accordingly, there is a need for techniques which allow for efficiently controlling radio communication in a cellular network supporting radio communication based different and potentially conflicting configurations.